Dental cement



I1 Patented May 27 1930 UNITED, 's l'a'ras I ctaanncn c. veer, or rrrrsncnerr, rmmsxnvnnm nnnrai. cnmnn'r I I0 Drawing.

The presentinvention 'relates to dental cement, and more especially to a dental 'cement inwhich the powder or a Substantial proportion of it is'reduced to grainsofcolr loidal dimensions. f

Practically all dental cements are marketed as a powder-ands. liquid which are to be mixed. by the dentist.

The powder consists of a basic material,

such as either'the black or the red oxide of copper in the oxyphosplrate of copper c.- ments; or ---zinc oxide modified by silica or bismuth oxide, or by long heating in the zinc oxyphospha-te "cements; .or. a calcium aluminum silicate along with other complex silicates, fluosilic'ates and phosphates in the silicate cements. q

The liquid is phosphoric acid.diluted in water an further modified by the addition of a sma amount ofsome metallic oxide or hydroxide, such as of zinc or aluminum.

The basic powder reacts with the acid liquid to form metallic phosphates in the first .two classes, and metallic phosphates along with other complex compounds in the silicate cements. These phosphates act as the cementing salts which bind the particles together and form the dental cement.

In the usual process of manufacturing, the dental cement powder is ground dry in a pebble mill, ball .mill or other suitable grinding device until the material lumps or cakes, to. such a degree that further grinding is not effective. The lumping or caking is caused by the finely ground material adhering to the sides of the mill orto the grinding balls or pebbles. The fine material adheres together and entraps air between the particles, which air forms a cushion which prevents finer grinding. After the material is ground until the lumping stage occurs, it is removed and sifted through a fine mesh sieve, usually about 300 meshesper inch.

. The material when examined under a microscope is found to consist practically entirely of fine grains or particles,'the dimensions of which are considerably larger than the colloidal dimensions. When a dental ce- 5 ment powder as heretofore made 'is thrown Application filed .1m 11,1926. Serial No. 128,713.."

part .of the powdered materialwill be of colloidal dimensions. When apowder :is I; 1 ground by my process-and thrown intowater 1 a a large proportion will remain-in permanent some of the basic material isremoved and into water practically all of the-powder will immediately settle out.

I have found that itispossible. its, these dental cement powders so that a 'arg'e 1 suspension, thus demonstrating that the par ticles are colloidal and are of sufficiently smallvdimensions to have a Brownian movement. The suspensionv also gives the dall effect upon the passage of a beam' light through the suspension.

I have found that the powder or-at least a, portion of the powder may "be reduced tocolloidal dimensions by wet grinding with a material which does not dissolve the powder or react with or peptize the particles. I have found that it is not practicable to use wetgrinding, using either water or alcohol as the liquid, because of the solvent action of these liquids on the dental cement powders. Because of the solvent action this interferes withthe setting of the cement. In addition, the peptiz ing action of the liquid makes the. separation of the colloidal parti- I cles from the solvent diflicult. T

I have found that by grinding the pow-- der in a liquid which is'not a solvent for the powder or does not react with or' peptize' theparticles, it is possible to. reduce their state of subdivision to practically colloidal dimensions.

v In my preferred embodiment I dry grind or .otherwise reduce the material to a fine. powder but of greater than colloidal dimensions, and then continue grinding in a suitable grinding mill, such as a pebble mill or other mill of-the ball type or in a colloid mill, in the presence of acetone. The acetone prevents the material from lumping or caking in the mill and allows the grinding to be continued until the powder or a con. siderable part of it is reduced to colloidal dimensions. The acetone, of course, prevents the air cushioning incident to dry grinding. The report-ion -ofthe powder which is reduced to grains of colloidal dimensions may" pared be controlled by the length of time of the wet grinding with the acetone. For commercial purposes the grinding should be continued until practically all of the material will pass readily through a sieve havin 500 meshes to the inch. Such material, whlle it may not have all of the powder reduced to colloidal dimensions, has a sufficient amount to give the beneficial effects hereinafter pointed out.

Another rough test in the case of the silicate powders is to try a little of the powder between the teeth. The silicate powders in dental cements as now made have a gritty feeling between the teeth, but when the silicate powder is ground according to my process the gritty feeling disappears entirely and the Ipowder has a smooth feeling between the teet After the grinding has been carried out to the desired degree, the mixture is drawn off from the mill. The greater part of the acetone removed by filtering and the residue gently heated to evaporate the acetone. The material is then ready to be packaged and sold for use in making dental cements.

I prefer to use acetone because it has no solvent action on the material. It does not tend to peptize or hold the finely ground material in suspension and is soluble in water, so that should a thin molecular film of acetone adhere to the particles of powder it would not interfere with the reaction between the powder and the liquid when the cement is mixed by the dentist. v

However, liquids other than acetone may be used, such, or example, as the petroleum products such as kerosene or naphtha. In case these are used the residue should be washed with some suitable solvent for the oil, such as acetone. Examples of other materials which may be used and which are sufliciently volatile so as not to require washing are ethyl ether and chlorinated hydrocarbons, such as dichlorethylene, carbon tetrachloride, chloroform, etc.

The powder having its grains or a considerable proportion of its grains of colloidal dimensions has certain valuable properties as a dental cement. It is known that the thinner the layer of the cementing material, the stronger the union between the two su stances being cemented together. Heretofore it has not been possible to make this layer of dental cement as thin as desirable because of the size of the particles of the powder, but in a dental cement powder preby my process all of the particles are either of. colloidal dimensions or sufiiciently a proaching colloidal dimensions to permit 0 a very much thinner layer than is possible with the dental cements as now manufactured. The adhesiveness of a dental cement is to a large extent dependent upon the amount of reaction possible between the powder, is in particles of.

der and the liquid during the mixing of the cement. By using a powder in WhlOh the grains or a considerable proportion of the grains are of colloidal dimensions, a much greater reaction is made possible between the powder and liquid than is sible 1n the dental cements as now manu actured. Also, because of the fineness of the particles, the cement, when it is set, is of a more homogeneous character and has greater strength and resistance to wear.

While the invention may be applied to the manufacture of all types of dental cements, it is particularly applicable to the manufacture of silicate cements. Heretofore silicate cements have not been satisfactory for cementing crowns, bridges and inlays because they were not as adhesive as the zinc cements. The silicate cements, however, have certain advantages over the zinc cements in that they are less soluble and are harder and more resistant to wear and are translucent. I have found that by grinding the powder for the silicate cement as herein described it is possible to increase the adhesiveness of the silicate cements to practically that of the oxyphosphate of zinc cements as now manufactured, thus producing a silicate cement having the well recognized advantages of insolubility, strength and translucence, combined with the necessary adhesive qualities for use cementing crowns, bridges, inlays and the The preparation of the silicate cement powder by my process also imparts other'advantageous characteristics to the silicate cement. It has been recognized by the dental profession that more pulps of filled teeth die under silicate fillings than under oxyphosphate of zinc fillings when the cements are used either as fillings or to cement inlays in place. The concensus of opinion'is that this is due to more free acid in the plastic silicate cements than in the zinc cements. The reaction between the basic powder and the acid liquid is proportional to the surface exposed by the particles. Therefore, when the powder, or a considerable proportion of the powcolloidal dimensions, there is a much more com lete neutralization of the acid in the-liquid tl an is possible with cement powders as now ground, and a silicate cement therefore may be put into the tooth containing no more uncombined acid than that of a zinc oxyphosphate cement.

While it is possible by my rocess to increase the adhesiveness of the si 'cate cements to practically that of the oxyphosphate of z 1nc cements as now manufactured, the adheslveness of the oxyphosphate of zinc cements or the copper cements may be increased greatly beyond the adhesiveness of those cements as now manufactured.

While I have specifically described the preferred embodiments and applications of my invention, it is to be understood that the invention is not so limited but may be otherwise embodied within the scope of the following claims.

I' claim:

1. A finely ground silicate dental cement powder of substantially uniform composition and having a sufficient proportion of the material in grains of colloidal dimensions to materially increase the adhesivenessof the cement.

2. A finely ground dental cement powder a of substantially uniform composition and having a suflicient proportion of the material in grains of colloidal dimensions to materially increase the adhesiveness of the cement.

In testimony whereof I have hereunto set my hand.

CLARENCE C. VOGT. 

